Synergism of Malathion and Parathion Against Resistant Insects: Phosphorus Esters with Synergistic Properties

Abstract

Many phosphorus esters were evaluated as synergists for malathion against resistant strains of the house fly, Musca domestica L., and the mosquito Culex tarsalis Coquillett. Several were tested as synergists for parathion against parathion-resistant house flies. S,S,S-and O,S,S-trialkyl and mixed alkyl phosphorothioites and phosphorothioates synergized malation and/or parathion against both insect species. With mosquitoes, butyl-containing esters were most effective; with flies esters containing isopropyl, propyl, or butyl groups were strongly synergistic. S,S-dialkyl O- or S-phenyl phosphorothioites also were active. O,O,O-triphenyl phosphorus compounds synergized malathion against both species; their S,S,S-triphenyl analogs were much less active. In general, tolyl and other substituted phenyl phosphates were malathion synergists against resistant mosquitoes only. The materials synergizing malathion against resistant insects differed considerably from those known to potentiate the toxicity of malathion to mice or to cause ataxia in chickens.